Dual mode plasma arc torch

ABSTRACT

A dual mode plasma arc torch and methods of operation thereof are provided, wherein the plasma arc torch is operable with both a high frequency power supply and a contact start power supply.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/183,693, filed Jul. 18, 2005, which is a continuation ofU.S. patent application Ser. No. 10/720,830, filed Nov. 24, 2003, nowU.S. Pat. No. 6,936,786, which is a continuation of U.S. patentapplication Ser. No. 10/083,029, filed Feb. 26, 2002, now U.S. Pat. No.6,717,096. The disclosures of the above applications are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates generally to plasma arc torches and moreparticularly to devices and methods for initiating a pilot arc in aplasma arc torch.

BACKGROUND OF THE INVENTION

Plasma arc torches, also known as electric arc torches, are commonlyused for cutting, marking, gouging, and welding metal workpieces bydirecting a high energy plasma stream consisting of ionized gasparticles toward the workpiece. In a typical plasma arc torch, the gasto be ionized is supplied to a distal end of the torch and flows past anelectrode before exiting through an orifice in the tip, or nozzle, ofthe plasma arc torch. The electrode has a relatively negative potentialand operates as a cathode. Conversely, the torch tip has a relativelypositive potential and operates as an anode. Further, the electrode isin a spaced relationship with the tip, thereby creating a gap, at thedistal end of the torch. In operation, a pilot arc is created in the gapbetween the electrode and the tip, which heats and subsequently ionizesthe gas. Ionized gas is then blown out of the torch and appears as aplasma stream that extends distally off the tip. As the distal end ofthe torch is moved to a position close to the workpiece, the arc jumpsor transfers from the torch tip to the workpiece because the impedanceof the workpiece to ground is lower than the impedance of the torch tipto ground. Accordingly, the workpiece serves as the anode, and theplasma arc torch is operated in a “transferred arc” mode.

One of two methods is typically used for initiating the pilot arcbetween the electrode and the tip. In the first method, commonlyreferred to as a “high frequency” or “high voltage” start, a highpotential is applied across the electrode and the tip sufficient tocreate an arc in the gap between the electrode and the tip. Accordingly,the first method is also referred to as a “non-contact” start, since theelectrode and the tip do not make physical contact to generate the pilotarc. In the second method, commonly referred to as a “contact start,”the electrode and the tip are brought into contact and are graduallyseparated, thereby drawing an arc between the electrode and the tip. Thecontact start method thus allows an arc to be initiated at much lowerpotentials since the distance between the electrode and the tip is muchsmaller.

Plasma arc torches, including the consumable components, e.g.,electrode, tip, are designed for either a contact start or a highfrequency start mode. Accordingly at least one plasma arc torch and aspecific set of consumables are used with a high frequency power supply,and at least one additional plasma arc torch and an additional set ofconsumables are used with a low voltage (contact start) power supply. Asa result, for an operator that uses both high frequency and low voltagepower supplies, a plurality of plasma arc torches and correspondingconsumables must be purchased and maintained in inventory for continuousoperations.

Accordingly, a need remains in the art to reduce the number of torches,parts, and consumables required for operation with a high frequency anda low voltage power supply. A further need exists to increase theefficiency of working with both a high frequency and a low voltage powersupply.

SUMMARY OF THE INVENTION

The present invention provides a plasma arc torch that is operable witheither a high frequency or a low voltage power supply, such that thetorch is capable of a high frequency start or a contact start, therebyresulting in a dual mode torch. Additionally, another dual mode torch isprovided that comprises a conventional contact start torch modified foroperation with a high frequency power supply. Yet another dual modetorch is provided that comprises a conventional high frequency starttorch modified for operation with a low voltage power supply.

In one preferred form, the present invention provides a dual mode plasmaarc torch that comprises an electrode, a tip, and a start cartridgedisposed between the electrode and the tip, wherein the start cartridgecomprises an initiator in electrical contact with the electrode and incontact with the tip. Accordingly, when the plasma arc torch is in acontact start mode, the initiator is movable to separate from the tipand establish a pilot arc between the initiator and the tip, and whenthe plasma arc torch is in a high frequency start mode, the startcartridge spaces the tip from the electrode such that a pilot arc isestablished between the electrode and the tip.

In another form, a plasma arc torch is provided that comprises anelectrode, a tip, and at least one of a contact start cartridge for acontact start mode and a high frequency start cartridge for a highfrequency start mode. When the plasma arc torch is in a contact startmode, the initiator is movable to separate from the tip and establish apilot arc between the initiator and the tip, and when the plasma arctorch is in a high frequency start mode, the high frequency startcartridge spaces the tip from the electrode such that a pilot arc isestablished between the electrode and the tip. Preferably, the highfrequency start cartridge comprises a plurality of vent holes thatprovide gas flow to cool the electrode, which are offset from a centerof the high frequency start cartridge in order to provide a swirlingflow and further cooling capability.

In yet another form, a conventional contact start plasma arc torch ismodified to comprise additional dielectric standoff, which is sized suchthat the contact start plasma arc torch may be operated under highfrequency. Additionally, a conventional high frequency plasma arc torchis modified to comprise a movable element, e.g., electrode, tip, orthird element, such that the high frequency plasma arc torch is operableunder low voltage, thereby resulting in dual mode torches, i.e. torchescapable of operating with either a high frequency or a low voltage powersupply. Additionally, methods of operating the dual mode plasma arctorches are provided in accordance with the teachings of the presentinvention.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a perspective view of a manually operated plasma arc apparatusin accordance with the principles of the present invention;

FIG. 2 is a side view of a torch head disposed within a plasma arc torchand constructed in accordance with the principles of the presentinvention;

FIG. 3 is a perspective view of a torch head constructed in accordancewith the principles of the present invention;

FIG. 4 is an exploded perspective view of a torch head and consumablecomponents constructed in accordance with the principles of the presentinvention;

FIG. 5 is a cross-sectional view of a torch head and consumablecomponents constructed in accordance with the principles of the presentinvention;

FIG. 6 is a plan view of a distal end of a torch head constructed inaccordance with the principles of the present invention;

FIG. 7A is a cross-sectional view of a torch head in an idle mode andconstructed in accordance with the principles of the present invention;

FIG. 7B is a cross-sectional view of a torch head in a pilot mode andconstructed in accordance with the principles of the present invention;

FIG. 8 is a cross-sectional view of a torch head comprising a startcartridge for a high frequency start mode and constructed in accordancewith the principles of the present invention;

FIG. 9 is an upper perspective view of a high frequency start cartridgeconstructed in accordance with the principles of the present invention;

FIG. 10 is a lower perspective view of the high frequency startcartridge in accordance with the principles of the present invention;

FIG. 11 is a plan view of the high frequency start cartridge inaccordance with the principles of the present invention;

FIG. 12 is a cross-sectional view, taken along line A-A of FIG. 11, ofthe high frequency start cartridge in accordance with the principles ofthe present invention;

FIG. 13A is a cross-sectional view of a torch head comprising andelectrode defining axial grooves and a second embodiment of a startcartridge for a high frequency start mode and constructed in accordancewith the principles of the present invention;

FIG. 13B s a cross-sectional view of a torch head comprising anelectrode defining spiral grooves and the second embodiment of a startcartridge for a high frequency start mode in accordance with theprinciples of the present invention;

FIG. 14 is a cross-sectional view of a prior art contact start plasmaarc torch;

FIG. 15 is a cross-sectional view of a contact start plasma arc torchmodified with additional dielectric standoff and constructed inaccordance with the principles of the present invention;

FIG. 16 is a cross-sectional view of a prior art high frequency startplasma arc torch; and

FIG. 17 is a cross-sectional view of a high frequency plasma arc torchretrofitted with a third element and constructed in accordance with theprinciples of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

Referring to the drawings, a dual mode torch according to the presentinvention is generally operable with a manually operated plasma arcapparatus as indicated by reference numeral 10 in FIG. 1. Typically, themanually operated plasma arc apparatus 10 comprises a plasma arc torch12 connected to a power supply 14 through a torch lead 16, which may beavailable in a variety of lengths according to a specific application.Further, the power supply 14 provides both gas and electric power, whichflow through the torch lead 16, for operation of the plasma arc torch12.

As used herein, a plasma arc apparatus, whether operated manually orautomated, should be construed by those skilled in the art to be anapparatus that generates or uses plasma for cutting, welding, spraying,gouging, or marking operations, among others. Accordingly, the specificreference to plasma arc cutting torches, plasma arc torches, or manuallyoperated plasma arc torches herein should not be construed as limitingthe scope of the present invention. Furthermore, the specific referenceto providing gas to a plasma arc torch should not be construed aslimiting the scope of the present invention, such that other fluids,e.g. liquids, may also be provided to the plasma arc torch in accordancewith the teachings of the present invention. Additionally, the terms“biased” or “biasing” should not be construed as meaning an electricalbias or voltage as often used in the electrical field.

Generally, three (3) preferred dual mode torch configurations aredisclosed in accordance with the teachings of the present invention,wherein the term “dual mode” refers to the ability of a single plasmaarc torch to operate in both a high frequency start mode and a contactstart mode. The first preferred dual mode torch comprises a startcartridge that is disposed between an electrode and a tip, in which oneor more start cartridges may be interchanged to operate the plasma arctorch in either a high frequency start mode or a contact start mode. Thesecond preferred dual mode torch is generally one among a plurality ofconventional contact start torches with a provision of additionalvoltage isolation, or dielectric standoff, between an anode body and acathode body. The third preferred dual mode torch configuration isgenerally one among a plurality of high frequency start torches with aprovision of a moving electrode, tip, and/or third element as describedin greater detail below.

Dual Mode Torch with Start Cartridge

Referring now to FIG. 2, a torch head for use in the contact startplasma arc torch 12 of the present invention is illustrated andgenerally indicated by reference numeral 20. As shown, the torch head 20defines a proximal end 22 that is disposed within a handle 24 (one halfof which is removed to show the details of construction) of the plasmaarc torch 12 and a distal end 26, to which a plurality of consumablecomponents are secured, as described in greater detail below. Theproximal end 22 is also adapted for connection to a torch lead 28, whichprovides both gas and electric power for operation of the contact startplasma arc torch 12. The connection to the torch lead 28 may comprise aquick disconnect such as that disclosed in co-pending application titled“Modular Plasma Arc Torch,” filed on Feb. 26, 2002, and commonlyassigned with the present application, the contents of which areincorporated herein by reference. Further, as described herein, proximaldirection or proximally is the direction towards the proximal end 22,and distal direction or distally is the direction towards the distal end26.

With reference to FIGS. 3 through 5, the torch head 20 further comprisesa housing 28 in which fixed components of the torch head 20 aredisposed. More specifically, the fixed components comprise a cathode 32(FIG. 5) that has relatively negative potential, an anode 34 that hasrelatively positive potential, and an insulating body 36 that insulatesthe cathode 32 from the anode 34. The consumable components aregenerally secured to the distal end 26 of the torch head 20 and comprisean electrode 38, a tip 40, a start cartridge 42 that is used to draw apilot arc as described below, and a shield cup 44 that secures theconsumable components to the distal end 26 of the torch head 20 andfurther insulates the consumable components from the surrounding areaduring operation of the torch. The shield cup 44 also positions andorients the consumable components, e.g., the start cartridge 42 and thetip 40, relative to one another for proper operation of the torch whenthe shield cup 44 is fully engaged with the torch head 20.

As further shown, the start cartridge 42, also referred to as a contactstart cartridge 42, comprises an initiator 50 and a coil spring 52housed within a cartridge body 54 and a tip seat 56. Accordingly, thestart cartridge 42 is preferably a single replaceable consumablecomponent. Additionally, the start cartridge 42 as shown is preferablyemployed with a contact start plasma arc torch, however, the startcartridge 42 may also be employed with a high frequency start plasma arctorch such that a single start cartridge is used for both high frequencyand contact start modes. However, additional configurations for thestart cartridge 42 specific to a high frequency start plasma arc torchare described in greater detail below.

The cartridge body 54 and the tip seat 56 together are referred to as acartridge assembly 55. In one form of the cartridge assembly 55, thecartridge body 54 is conductive while the tip seat 56 is insulative. Inanother form of the cartridge assembly 55, the cartridge body 54 isinsulative, the tip seat 56 is insulative, and the cartridge assemblyfurther comprises a conductive member 53, which may be a washer asshown, disposed at a proximal end of the cartridge body 54. The functionand operation of the start cartridge 42, its components, and the fixedand other consumable components of the torch head 20 are described ingreater detail below.

As shown in FIG. 5, the torch head 20 is illustrated with the cathode 32secured within the housing 28, and the electrode 38 electricallyconnected to the cathode 32. The generally cylindrical insulating body36 surrounds the cathode and insulates the cathode 32 from the anode 34.As further shown, the cathode 32 abuts and electrically connects with apin fitting 64 that is adapted for connection to the torch lead 28 (notshown). Accordingly, the cathode 32 is electrically connected to thenegative side of the power supply 14 (not shown), and the anode 34 is inelectrical communication with the positive side of the power supply.Further, the pin fitting 64 defines an internal bore 66 and the cathode32 defines a central bore 70, which are in fluid communication for thesupply of a working gas from the power supply 14 to the torch head 20.Although the cathode 32 and the pin fitting 64 are illustrated as beingoriented at an angle relative to one another, the cathode 32 and the pinfitting 64 (or another adjacent component connected to the cathode 32)may alternately be colinear, or oriented 180 degrees relative to oneanother as commonly referred to in the art.

The electrode 38 defines an upper connecting end 72 for connecting theelectrode 38 with a connecting end 74 of the cathode 32. The connectingends 72, 74 of the electrode 38 and the cathode 32 are configured forcoaxial telescoping connection with one another as shown and describedin co-owned U.S. Pat. No. 6,163,008, which is incorporated herein byreference. To establish the connection between the cathode 32 and theelectrode 38, the cathode connecting end 74 and the electrode connectingend 72 are formed with opposing detents generally designated 76 and 78,respectively. The detents 76 and 78 are interengageable with one anotherwhen the connecting end 74 of the electrode 38 is connected to thecathode 32 to inhibit axial movement of the electrode 38 away from thecathode 32. However, it should be understood that the electrode 38 maybe connected to the cathode 32 in other conventional manners, such as bya threaded connection, without departing from the scope of the presentinvention.

Additionally, an insulating body 80 is disposed in the proximal end ofthe cathode 32, and an insulating cap 82 is mounted on the distal end ofthe cathode 32, which results in a relatively small area within thecathode central bore 70 exposed for contacting the electrode 38. Boththe insulating body 80 and the insulating cap 82 are configured andpositioned to inhibit electrical contact between an object other thanthe electrode 38 with the cathode 32 to reduce the risk of torchmalfunction should such an object be inserted into the cathode centralbore 70.

The electrode 38 defines a central bore 84 that extends distally fromthe connecting end 72 and is in fluid communication with the centralbore 70 of the cathode 32 such that the working gas in the cathodecentral bore 70 is directed down through the central bore 84 of theelectrode 38. The central bore 84 of the electrode 38 extends distallyfrom the connecting end 72 into registry with gas distributing holes 86that extend radially outward from the central bore 84 for exhaustingworking gas from the electrode 38. The electrode 38 further comprises anannular collar 88 that extends radially outward as shown and defines aproximal shoulder 90 below the gas distributing holes 86. The proximalshoulder 90 abuts a bushing 92 that is seated within an annular groove94 formed in the insulating body 36. The bushing 92 is a durablematerial, preferably a polyimide such as Vespel®, so that the torch head20 can withstand repeated installation of an electrode 38 withoutcausing damage to the insulating body 36, which is more costly anddifficult to replace. Further, a distal portion 96 of the electrode 38defines a generally elongated, cylindrical shape with a fluted surfaceformed by longitudinally extending ridges 98. The electrode 38 of theillustrated embodiment is constructed of copper or a copper alloy andpreferably comprises an emissive insert 100 secured within a recess 102at the distal end of the electrode 38.

The generally hollow tip 40, also commonly referred to as a nozzle, ismounted over the distal portion 96 of the electrode 38. The tip 40 is ina radially and longitudinally spaced relationship with the electrode 38to form a primary gas passage 104, which is also referred to as an arcchamber or plasma chamber. A central exit orifice 106 of the tip 40communicates with the primary gas passage 104 for exhausting ionized gasin the form of a plasma stream from the tip 40 and directing the plasmastream down against a workpiece. The tip 40 further comprises a hollow,generally cylindrical distal portion 108 and an annular flange 110 at aproximal end 112. The annular flange 110 defines a generally flat,proximal face 114 that seats against and seals with the tip seat 56 ofthe start cartridge 42, and a distal face 116 adapted to seat within andmake electrical contact with a conductive insert 118 disposed within theshield cup 44. The conductive insert 118 is further adapted forconnection with the anode 34, preferably using a threaded connection 119such that electrical continuity between the positive side of the powersupply is maintained. Accordingly, the tip 40 is in electrical contactwith the positive, or anode, side of the power supply through theconductive insert 118.

The tip 40 further defines a plurality of swirl holes 120 (further shownin FIG. 4) offset from a center of the tip 40 and positioned around andthrough the annular flange 110. Additionally, the tip 40 preferablydefines a plurality of secondary gas holes 122 (also shown in FIG. 4)extending radially through the annular flange 110 and into an annularrecess 124 on the distal face 116. Accordingly, the tip 40 regulates theplasma gas to form a plasma stream in addition to the secondary gas tostabilize the plasma stream, which is further shown and described inco-pending application titled “Tip Gas Distributor,” filed on Feb. 26,2002, and commonly assigned with the present application, the contentsof which are incorporated herein by reference. Further, the tip 40 ispreferably made of a copper or copper alloy material.

The shield cup 44 surrounds the distal end 26 of the torch head 20 andgenerally secures and positions the consumable components therein, inaddition to insulating an area surrounding the torch head 20 from theconductive components during operation and while the power supply 14(not shown) supplies electric power to the torch head 20. When securedto the torch head 20 through the threaded connection 119, a primary gaschamber 126 is formed between the conductive insert 118 of the shieldcup 44 and the insulating body 36, the start cartridge 42, and the tip40, through which the primary working gas flows during operation of thetorch as described in greater detail below. Additionally, the shield cup44 is preferably made of a non-conductive, heat insulating material,such as a phenolic or ceramic.

The insulating body 36 further defines a plurality of radial gasdistributing holes 128 that are in fluid communication with theelectrode gas distributing holes 86 and also with the primary gaschamber 126. Referring also to FIG. 6, the insulating body 36 furtherdefines a plurality of axial vent holes 130 extending through a distalface 132, which are in fluid communication with a set of radial ventholes 134 defined in a proximal section 136 of the insulating body 36.The radial vent holes 134 are in further fluid communication with a setof radial vent holes 138 defined in a distal section 140 of the anodemember 34, which are in fluid communication with an opening 142 near theproximal end of the shield cup 44, formed between the shield cup 44 andthe torch head housing 28, which is exposed to atmosphere as shown.Accordingly, gas is vented through the series of vent holes in theinsulating body 36, the anode 34, and the shield cup 44 during operationof the torch is described in greater detail below. Further, theinsulating body 36 is preferably made of a non-conductive, heatinsulating material, such as phenolic or ceramic, and the anode member34 is made of a conductive material such as brass or a brass alloy.

Referring to FIGS. 7A and 7B, the start cartridge 42 in accordance withthe principles of the present invention is operable between an idle mode(FIG. 7A) and a pilot mode (FIG. 7B) of the torch. In the idle mode, theinitiator 50 is in electrical contact with the electrode 38 and isresiliently biased into contact with the tip 40. The initiator 50preferably defines a beveled distal contact surface 152 that is incontact with a conical interior surface 154 of the tip 40. Further, theinitiator 50 is resiliently biased into contact with the tip 40 with anysuitable biasing member or means, such as a spring, or an elastic orelastomeric member, among others. In the preferred embodiment as shown,the biasing member is the coil spring 52, which is sufficiently stiffthat gas pressure from the gas supply overcomes the spring force toseparate the initiator 50 from the tip 40. Further, the initiator 50 andthe coil spring 52, along with the cartridge body 54 and the tip seat56, are preferably part of a replaceable start cartridge 42.Accordingly, the tip seat 56 defines an annular shoulder 57 that engagesan annular flange 59 of the cartridge body 54, wherein the connectionbetween the annular shoulder 57 and the annular flange 59 may be pressfit or adhesively bonded, among other methods commonly known in the art.

As further shown, the cartridge body 54 comprises a recessed end wall155 that abuts a distal shoulder 156 of the electrode 38, and agenerally cylindrical sidewall 158. When fully assembled, a chamber 160is defined within the start cartridge 42, in which the coil spring 52and a portion of the initiator 50 are disposed. The cartridge body 54further defines axial vent holes 162 that extend through the recessedend wall 155 and that are in fluid communication with the chamber 160and with the axial vent holes 130 in the distal face 132 of theinsulating body 36 as previously described. Additionally, a series ofradial gas holes 164 are disposed around the sidewall 158, which directa portion of the working gas into the start cartridge 42 to overcome thebias of coil spring 52 to move the initiator 50 away from the tip 40 andagainst the bias of the coil spring 52 as described in greater detailbelow.

The initiator 50 defines a generally cylindrical portion 166, an annularflange 168, and a tubular portion 170 that defines the beveled contactsurface 152. As shown, the proximal section of the tubular portion 170is in electrical contact with the electrode 38, and the distal sectionof the tubular portion 170 projects distally through a central aperture172 in the tip seat 56. Further, the coil spring 52 is disposed withinthe cylindrical portion 166 and is seated against a proximal face 174 ofthe initiator. The proximal face 174 further defines axial vent holes175, which are in fluid communication with the chamber 60 and also withthe cartridge body axial vent holes 162, such that the gas in thechamber is vented from the torch head 20 as further described below.Preferably, the initiator 50 is made of a conductive material such ascopper or a copper alloy, the coil spring 52 is made of a steelmaterial, the cartridge body 54 is made of a conductive material such asbrass, and the tip seat 56 is made of a nonconductive material such as apolyimide. Alternately, as previously set forth, the cartridge body 54may be insulative, or nonconductive, while the tip seat 56 isinsulative.

The initiator 50 according to the present invention is free from fixedconnection to the electrode 38 and the cathode 32 (i.e., the cathodeside) and the anode 34, the conductive insert 118, and the tip 40 (i.e.,the anode side). The term “free from fixed connection” as used hereinmeans that relative movement is possible between the initiator 50 andthe cathode side and the anode side in at least one direction, such asaxially and/or radially. For example, in the illustrated embodiment, theinitiator 50 is free to move axially along a central longitudinal axis Xof the torch head 20 within the chamber 160 of the start cartridge 42.More particularly, the initiator 50 is axially movable relative to theelectrode 38 and the tip 40 between a first, distal position (FIG. 7A)corresponding to the idle mode of the torch, and a second, proximalposition (FIG. 7B) corresponding to the pilot mode of the torch.However, it should be understood that the initiator 50 may be free tomove radially relative to the cathode side and the anode side. It isalso understood that the initiator 50 may instead be stationary withinthe torch and either the cathode side, the anode side, or both may befree to move, axially and/or radially, relative to the initiator 50.

As further shown, a plurality of 0-rings and associated o-ring groovesare disposed within the torch head 20 to seal the gas flow duringoperation of the torch. More specifically, an o-ring 180 is disposedbetween the insulating body 36 and the start cartridge 42 at the distalend 150 of the insulating body 36. Additionally, an o-ring 182 isdisposed between the anode 34 and the conductive insert 118 of theshield cup 44 near the distal section 140 of the anode 34. Accordingly,the o-rings 180 and 182 seal the gas flow within the torch head 20during operation.

Referring to FIGS. 7A and 7B, which correspond with the idle mode of thetorch and the pilot mode of the torch, respectively, the operation ofthe start cartridge 42, and more specifically the initiator 50, toinitiate a pilot arc and to operate the torch according to a method ofthe present invention is shown and described in greater detail. Asillustrated, the torch head 20 is connected to a supply of gas andelectric power, preferably through the pin fitting 64 as previouslydescribed. The application of electric power causes current to flow fromthe electrode 38, through the initiator 50, and to the tip 40, which areall in direct electrical connection. When the gas supply is activated, aworking gas flows through the internal bore 66 of the pin fitting 64 andthrough the central bores 70 and 84 of the cathode 32 and the electrode38, respectively. The gas then flows through gas distributing holes 86of the electrode 38 and through gas distributing holes 128 of theinsulating body 36, which causes the gas flow distally into the primarygas chamber 126. The gas then partially flows through the radial gasholes 164 of the start cartridge 42, which causes the initiator 50 tomove proximally away from the tip 40, as shown in FIG. 7B in the pilotmode of the torch. Accordingly, the gas pressure is sufficiently high toovercome the bias of the coil spring 52. As the initiator 50 movesproximally away from the tip 40, a pilot arc is drawn between theinitiator 50 and the tip 40, and more specifically between the conicalinterior surface 154 and the beveled distal contact surface 152 whichare configured relatively parallel to one another as shown.

Further to the gas flowing partially through the radial gas holes 164 tomove the initiator 50, the gas continues to flow distally and into swirlholes 120 as the plasma gas and also into the secondary gas holes 122 asthe secondary gas. Accordingly, the plasma gas swirls in the gap betweenthe initiator 50 and the tip 40 and is ionized by the pilot arc formedbetween the initiator 50 and the tip 40. As shown, the swirl holes 120are preferably positioned proximally from the area where the conicalinterior surface 154 of the initiator 50 contacts the beveled distalcontact surface 152 of the tip 40, in order to provide a more stableplasma stream. However, the swirl holes 120 may be positioned distallyfrom the area where the initiator 50 contacts the tip 40 and remainwithin the scope of the present invention. As a result of the gasswirling and pilot arc creation, the ionized gas is blown out thecentral exit orifice 106 of the tip 40 in the form of a plasma stream.Additionally, the gas that flows through the secondary gas holes 122flows into the annular recess 124 and then distally along the generallycylindrical distal portion 108 of the tip 40. As a result, the secondarygas forms a cylindrical gas envelope to stabilize the plasma stream thatis blown from the central exit orifice 106. The tip 40 with the swirlholes 120 and the secondary gas holes 122 is further described in theco-pending application titled “Tip Gas Distributor,” filed Feb. 26,2002, and commonly assigned with the present application, the contentsof which are incorporated herein by reference.

As further shown, the gas that flows into the start cartridge 42 to movethe initiator 50 proximally away from the tip 40 is vented through theaxial vent holes 175 of the initiator, through axial vent holes 162 inthe annular end wall 155 of the cartridge body 54, and proximallythrough the axial vent holes 130 (shown dashed) in the insulating body36. The gas then flows through the radial vent holes 134 in theinsulating body 36, through the radial vent holes 138 in the anode 34,and out through the opening 142 at the proximal end of the shield cup44. Accordingly, the torch head 20 according to the present inventionincorporates head vent holes (i.e., radial vent holes 134, 138) to ventgas from the torch head 20, which facilitates a more rapid restart ofthe torch after the gas and electric power are turned off. When the gasand electric power are turned off and the gas is vented as previouslydescribed, the force of the coil spring 52 causes the initiator 50 tomove distally towards the tip 40 such that the conical interior surface154 and the beveled distal contact surface 152 come into contact,wherein the plasma arc torch is in the idle mode.

Additional configurations for the start cartridge 42 with the movinginitiator 50 may also be employed in accordance with the teachings ofcopending application titled “Contact Start Plasma Arc Torch and Methodof Initiating a Pilot Arc,” filed Feb. 26, 2002, which is commonlyassigned with the present application and the contents of which areincorporated herein by reference.

Referring now to FIGS. 8 through 12, a start cartridge 200 for use in ahigh frequency start torch, also referred to as a high frequency startcartridge 200, is shown and is disposed between the electrode 38 and thetip 40 within the torch head 20. The start cartridge 200 defines agenerally cylindrical outer wall 202 with a recessed proximal face 204and a recessed distal face 206. Further, the start cartridge 200comprises an internal collar 208, wherein a venting chamber 210 isformed between the internal collar 208 and the proximal face 204 asshown. Moreover, the internal collar 208 isolates the venting chamber210 from the plasma chamber 104 during operation of the plasma arctorch.

The start cartridge 200 further comprises a plurality of vent passages212 formed in the proximal face 204 that are in communication with theventing chamber 210 and the axial vent holes 130 (shown dashed) formedin the insulating body 36 as previously described. As further shown, thedistal shoulder 156 of the electrode 38 abuts the proximal face 204 ofthe start cartridge 200, while a distal shaft 214 of the electrode 38 isslidably engaged within the internal collar 208. Additionally, the tip40 abuts the recessed distal face 206 as shown when the components ofthe torch head 20 are secured to the torch head 20 by the shield cup 44.

The start cartridge 200 also comprises a plurality of vent holes 216,which are preferably offset from a center of the start cartridge 200 asbest illustrated in FIG. 11. As shown, a total of six (6) vent holes 216are provided, however, one or more vent holes 216 may be providedaccording to specific operational requirements. The vent holes 216 alsodefine outer vent holes 216 a and inner vent holes 216 b, wherein theinner vent holes 216 b are generally smaller in diameter than the outervent holes 216 a such that a pressure drop is created through the ventholes 216 and the velocity of the gas is thereby increased for purposesas set forth below. Further, the vent passages 212 preferably define apartial cylindrical configuration that are in fluid communication withthe venting chamber 210 extending through the start cartridge 200.Additionally, a total of three (3) vent passages 212 are employed in oneform of the present invention, however, one or more vent passages 212may be used according to specific operational requirements.

In operation, a portion of the working gas that flows distally throughthe primary gas chamber 126 flows into the vent holes 216 to create aswirling flow of gas within the venting chamber 210. The gas then flowsfrom the venting chamber 210 through the vent passages 212 and throughthe axial vent holes 130 to vent through the torch head as previouslydescribed. Accordingly, the vent holes 216 provide a passage for gas tocool the electrode 38 during operation of the plasma arc torch.Additionally, as the gas flows from the outer vent holes 216 a to theinner vent holes 216 b, the velocity increases, thereby providingadditional cooling for the electrode 38.

Preferably, the start cartridge 200 is a molded, single-piece componentand is nonconductive or insulative. Accordingly, the preferred materialfor the start cartridge 200 is Delrin®, or other similar nonconductivematerial commonly known in the art such as Nylon or Vespel®.Additionally, the vent holes 216 a and 216 b may be secondarily formedthrough the start cartridge 200 using methods such as high-precisionmachining, among others commonly known in the art.

Referring now to FIGS. 13A and 13B, the central portion 206 of theelectrode 38 may be configured to provide additional cooling, as shownby electrodes 38′ (FIG. 13A) and 38″ (FIG. 13B), wherein the centralportion 206 may define axial grooves 220 (FIG. 13A) or spiral grooves222 (FIG. 13B) as shown. Accordingly, the grooves 220 and 222 direct andcontrol the gas being vented through the start cartridge 200 along thecentral portion 206 of the electrode 38 to provide additional cooling asnecessary. Additionally, the internal collar 208 may be positionedfurther distally within the start cartridge 200 as shown to minimize anyupward flow of the plasma gas being swirled into the plasma chamber 104by the tip 40.

Contact Start Torch Operable under High Frequency

As a result of previously described embodiments wherein the startcartridge having an initiator is operable under both low voltage andhigh frequency, the inventors have further developed torch embodimentswherein a conventional contact start torch is operable under highfrequency. Generally, an additional amount of dielectric standoff isprovided between a cathode body and an anode body within the torch headsuch that the high frequency, or high voltage, does not penetrate or arcthrough the insulating body and cause the torch to malfunction. Further,any additional moving elements, e.g., electrode, tip, and/or movingthird element, as described in greater detail below, operatesubstantially the same as under low voltage.

Referring to FIG. 14, a conventional contact start torch 230 isillustrated, wherein an electrode 232 is movable against a spring member234 to initiate a pilot arc between the electrode 232 and a tip 236. Asshown, the contact start torch 230 comprises a cathode body 238, ananode body 240, and insulating bodies 242 and 244 disposed between thecathode body 238 and the anode body 240, wherein the cathode body 238further includes the electrode 232 as the negative side of the powersupply, and the anode body 240 further includes the tip 236 and a cap246 as the positive side of the power supply. However, if a highfrequency were to be supplied to the contact start torch 230, the highvoltage would likely arc across the cathode body 238 and the anode body240, most likely in the area designated by “A,” which would probablycause the contact start torch 230 to malfunction.

Referring now to FIG. 15, additional dielectric standoff is providedwithin the conventional contact start torch 230, wherein the insulatingbodies 242 and 244 are substantially thicker in cross section so as toprevent such arcing and the likelihood of torch malfunction.Accordingly, the size of the tip 236 and the cap 246 are also increasedto accommodate the additional dielectric standoff, in the form ofthicker insulating bodies 242 and 244, as shown.

High Frequency Torch Operable under Low voltage

As a result of previously described embodiments wherein the startcartridge having an initiator is operable under both low voltage andhigh frequency, the inventors have further developed torch embodimentswherein a conventional high frequency start torch is operable under lowvoltage. Generally, the high frequency start torch is retrofitted with amoving element such as a moving electrode, a moving tip, and/or a movingthird element as described in greater detail below. Accordingly, thehigh frequency plasma arc torch maintains a configuration with a highdegree of dielectric standoff, and the moving element is used to draw apilot arc for ignition of the high frequency plasma arc torch under lowvoltage.

Referring to FIG. 16, a conventional high frequency start torch 260 isillustrated, which is shown and described in co-owned U.S. Pat. No.6,163,008, the contents of which are incorporated herein by reference.As shown, the high frequency torch 260 comprises a dielectric standoff,i.e. insulating body 262, sufficient to withstand a high frequencystart, however, none of the components are movable and thus the torch asshown cannot operate under low voltage.

Referring now to FIG. 17, the high frequency torch 260 is illustratedwith a movable element 264, which is shown biased into contact with anelectrode 266 and movable against the bias towards a tip 268 such that apilot arc is drawn between the electrode 266 and a tip 268. It should beunderstood by those skilled in the art that the movable element 264 maycomprise a movable electrode, a movable tip, and/or a movable thirdelement, such as those described in U.S. Pat. No. 5,994,663 (movingthird element), U.S. Pat. No. 4,902,871 (moving electrode), and U.S.Pat. No. 5,897,795 (moving nozzle), among others commonly known in theart. Accordingly, the high frequency torch 260 is retrofitted with amovable element 264 such that the high frequency torch 260 is operableunder low voltage.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the substance of the inventionare intended to be within the scope of the invention. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention.

1. A method of operating a plasma arc torch comprising disposing atleast one dielectric standoff within the plasma arc torch such that theplasma arc torch is operable with both a high frequency power supply anda contact start power supply.
 2. The method according to claim 1,wherein the dielectric standoff is disposed within a group consisting ofa torch head, a torch lead, a torch handle, consumable components, aconnector, an adapter, and a power supply.
 3. A method of operating aplasma arc torch comprising disposing at least one component within theplasma arc torch, the component sized to provide additional voltageisolation such that the plasma arc torch is operable with both a highfrequency power supply and a contact start power supply.
 4. The methodaccording to claim 3, wherein the component is selected from a groupconsisting of a torch head, a torch lead, a torch handle, consumablecomponents, a connector, an adapter, and a power supply.
 5. The methodaccording to claim 3, wherein the component is a consumable componentselected from the group consisting of an electrode, a start cartridge, agas distributor, a tip, a spring, and a shield cup.
 6. A method ofoperating a plasma arc torch, wherein the plasma arc torch is operablewith both a high frequency power supply and a contact start powersupply.
 7. The method according to claim 6 further comprising disposinga set of consumables within a plasma arc torch, the set of consumablesbeing sized to provide additional voltage isolation such that the set ofconsumables are operable under both contact start and high frequencystart modes of the plasma arc torches.
 8. The method according to claim7, wherein the consumables are selected from the group consisting of anelectrode, a start cartridge, a gas distributor, a tip, a spring, and ashield cup.
 9. A plasma arc torch that is operable with both a highfrequency power supply and a contact start power supply.